kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 170 insertions, 0 deletions

diff --git a/include/net/strparser.h b/include/net/strparser.h
new file mode 100644
index 000000000..0ed73e364
--- /dev/null
+++ b/include/net/strparser.h
@@ -0,0 +1,170 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Stream Parser
+ *
+ * Copyright (c) 2016 Tom Herbert <tom@herbertland.com>
+ */
+
+#ifndef __NET_STRPARSER_H_
+#define __NET_STRPARSER_H_
+
+#include <linux/skbuff.h>
+#include <net/sock.h>
+
+#define STRP_STATS_ADD(stat, count) ((stat) += (count))
+#define STRP_STATS_INCR(stat) ((stat)++)
+
+struct strp_stats {
+	unsigned long long msgs;
+	unsigned long long bytes;
+	unsigned int mem_fail;
+	unsigned int need_more_hdr;
+	unsigned int msg_too_big;
+	unsigned int msg_timeouts;
+	unsigned int bad_hdr_len;
+};
+
+struct strp_aggr_stats {
+	unsigned long long msgs;
+	unsigned long long bytes;
+	unsigned int mem_fail;
+	unsigned int need_more_hdr;
+	unsigned int msg_too_big;
+	unsigned int msg_timeouts;
+	unsigned int bad_hdr_len;
+	unsigned int aborts;
+	unsigned int interrupted;
+	unsigned int unrecov_intr;
+};
+
+struct strparser;
+
+/* Callbacks are called with lock held for the attached socket */
+struct strp_callbacks {
+	int (*parse_msg)(struct strparser *strp, struct sk_buff *skb);
+	void (*rcv_msg)(struct strparser *strp, struct sk_buff *skb);
+	int (*read_sock)(struct strparser *strp, read_descriptor_t *desc,
+			 sk_read_actor_t recv_actor);
+	int (*read_sock_done)(struct strparser *strp, int err);
+	void (*abort_parser)(struct strparser *strp, int err);
+	void (*lock)(struct strparser *strp);
+	void (*unlock)(struct strparser *strp);
+};
+
+struct strp_msg {
+	int full_len;
+	int offset;
+};
+
+struct _strp_msg {
+	/* Internal cb structure. struct strp_msg must be first for passing
+	 * to upper layer.
+	 */
+	struct strp_msg strp;
+	int accum_len;
+};
+
+struct sk_skb_cb {
+#define SK_SKB_CB_PRIV_LEN 20
+	unsigned char data[SK_SKB_CB_PRIV_LEN];
+	/* align strp on cache line boundary within skb->cb[] */
+	unsigned char pad[4];
+	struct _strp_msg strp;
+
+	/* strp users' data follows */
+	struct tls_msg {
+		u8 control;
+	} tls;
+	/* temp_reg is a temporary register used for bpf_convert_data_end_access
+	 * when dst_reg == src_reg.
+	 */
+	u64 temp_reg;
+};
+
+static inline struct strp_msg *strp_msg(struct sk_buff *skb)
+{
+	return (struct strp_msg *)((void *)skb->cb +
+		offsetof(struct sk_skb_cb, strp));
+}
+
+/* Structure for an attached lower socket */
+struct strparser {
+	struct sock *sk;
+
+	u32 stopped : 1;
+	u32 paused : 1;
+	u32 aborted : 1;
+	u32 interrupted : 1;
+	u32 unrecov_intr : 1;
+
+	struct sk_buff **skb_nextp;
+	struct sk_buff *skb_head;
+	unsigned int need_bytes;
+	struct delayed_work msg_timer_work;
+	struct work_struct work;
+	struct strp_stats stats;
+	struct strp_callbacks cb;
+};
+
+/* Must be called with lock held for attached socket */
+static inline void strp_pause(struct strparser *strp)
+{
+	strp->paused = 1;
+}
+
+/* May be called without holding lock for attached socket */
+void strp_unpause(struct strparser *strp);
+
+static inline void save_strp_stats(struct strparser *strp,
+				   struct strp_aggr_stats *agg_stats)
+{
+	/* Save psock statistics in the mux when psock is being unattached. */
+
+#define SAVE_PSOCK_STATS(_stat) (agg_stats->_stat +=		\
+				 strp->stats._stat)
+	SAVE_PSOCK_STATS(msgs);
+	SAVE_PSOCK_STATS(bytes);
+	SAVE_PSOCK_STATS(mem_fail);
+	SAVE_PSOCK_STATS(need_more_hdr);
+	SAVE_PSOCK_STATS(msg_too_big);
+	SAVE_PSOCK_STATS(msg_timeouts);
+	SAVE_PSOCK_STATS(bad_hdr_len);
+#undef SAVE_PSOCK_STATS
+
+	if (strp->aborted)
+		agg_stats->aborts++;
+	if (strp->interrupted)
+		agg_stats->interrupted++;
+	if (strp->unrecov_intr)
+		agg_stats->unrecov_intr++;
+}
+
+static inline void aggregate_strp_stats(struct strp_aggr_stats *stats,
+					struct strp_aggr_stats *agg_stats)
+{
+#define SAVE_PSOCK_STATS(_stat) (agg_stats->_stat += stats->_stat)
+	SAVE_PSOCK_STATS(msgs);
+	SAVE_PSOCK_STATS(bytes);
+	SAVE_PSOCK_STATS(mem_fail);
+	SAVE_PSOCK_STATS(need_more_hdr);
+	SAVE_PSOCK_STATS(msg_too_big);
+	SAVE_PSOCK_STATS(msg_timeouts);
+	SAVE_PSOCK_STATS(bad_hdr_len);
+	SAVE_PSOCK_STATS(aborts);
+	SAVE_PSOCK_STATS(interrupted);
+	SAVE_PSOCK_STATS(unrecov_intr);
+#undef SAVE_PSOCK_STATS
+
+}
+
+void strp_done(struct strparser *strp);
+void strp_stop(struct strparser *strp);
+void strp_check_rcv(struct strparser *strp);
+int strp_init(struct strparser *strp, struct sock *sk,
+	      const struct strp_callbacks *cb);
+void strp_data_ready(struct strparser *strp);
+int strp_process(struct strparser *strp, struct sk_buff *orig_skb,
+		 unsigned int orig_offset, size_t orig_len,
+		 size_t max_msg_size, long timeo);
+
+#endif /* __NET_STRPARSER_H_ */